Angle detection method for bending machine, angle detection apparatus and angle sensor

ABSTRACT

An angle detection method for a bending machines for detecting a bending angle of a bent workpiece and an angle detection apparatus and an angle sensor thereof are provided. A detection light is emitted toward a workpiece W from a light source  9  while the angle sensor  3  is rotated in the forward and reverse directions. A plurality of optical sensors  11, 13  arranged at mutually symmetrical positions with the light source  9  being at the center thereof receive the reflection light from the measurement object W. The quantity of received light is stored in relation to the rotation angle of the angle sensor  3  detected by an rotation angle detector  33 . A angle calculation portion  35  calculates the angle of the measurement object W based on the peak values of the data of the quantity of the received light and the rotation angles of the angle sensor  3  corresponding to the peak values. Alternatively, the rotation angle detector  3  detects the rotation angles of the angle sensor  3  at the time when the quantities of the received light received by the pair of optical sensors  11, 13  are the same, and the angle calculation portion  33  calculates the angle of the measurement object W based on the rotation angles.

FIELD OF TECHNOLOGY

This invention relates to a method and apparatus, and to an angle sensorused in the apparatus, for detecting the bending angle of a plate-shapedworkpiece bent by a bending processing machine such as a press brake forexample.

BACKGROUND TECHNOLOGY

FIG. 13 shows one example structure from the prior art for detecting thebending angle 2 θ of a measurement object comprised of a workpiece Wwhich has undergone a bending process in cooperation with a punch P anda die D equipped in a press brake (omitted from the drawings), whereinan upward bend angle 2 θ is determined by raising or lowering adetection element 101 to bring the tip of the detection element 101 intocontact with a lower surface of the workpiece W, with this value thenbeing doubled to determine the bending angle 2 θ.

In the above-described structure of an angle detection apparatus 103, anascension/descension device 107 such as a cylinder is provided on a diebase 105 equipped with a die D, and by means of thisascension/descension device 107 the detection element 101 is raised inan upward direction in FIG. 13 to be brought into contact with a lowersurface of the workpiece W. The raised position of the detection elementat this time can be measured, for example, by a pulse encoder 113connected to a pinion gear 111 which meshes with a rack 109 arranged tomove up and down together with the detection element 101, whereby astructure is formed for detecting the bending angle 2 θ.

Further, a process for detecting the bending angle of the workpiece maybe carried out by imaging an edge surface of the bent up workpiece witha non-contact imaging means and then processing such imaged data with aimage processing.

Furthermore, there is another angle measurement apparatus, in which arotatable frame equipped with a light source and a converging lens isprovided, and in which a plurality of light-receiving elements arearranged in the shape of a circular arc at a location corresponding tothe focus position of the converging lens, whereby reflected light ofthe light which emitted toward the workpiece from the light source isfocused by the converging lens toward the position of thelight-receiving elements arranged in the shape of the circular arc,whereby the position of the light-receiving elements where the receivedlight is a maximum is detected in order to detect the bending angle ofthe workpiece.

However, there is a problem with regards to these types of prior arttechnology in that highly accurate angle detection is difficult becausethe bending angle is determined from the relationship between theposition of the die D and the position of the workpiece W determined bymeasuring the position of the detection element 101 in contact with theworkpiece W.

Further, because angle detection is carried out by bringing thedetection element 101 into contact with the workpiece W, deformation ofthe workpiece W will arise depending on the strength of contact with thedetection element, and this risk of changes arising in the bending anglecreates a problem.

Further, in the case where an image processing device is used, becausethe apparatus is a non-contact type, there is no risk of changes arisingdue to contact, but high costs and the ability to only measure an edgesurface of the workpiece creates problems.

In the structure having a plurality of light-receiving elements arrangedin a circular arc shape at positions corresponding to the focus of therotating converging lens, because accurate measurements are difficult ifthe light-receiving elements are shifted even a small amount from thefocus position of the converging lens, there is a need for highprecision in the apparatus and this creates problems.

In view of the problems of the prior art described above, it is anobject of the present invention to provide an angle detection method forbending machines, an angle detection apparatus and an angle sensor whichmake it possible to carry out highly accurate angle detection bydetecting the angle of a bent workpiece without making contact with thesurface of the workpiece.

DISCLOSURE OF THE INVENTION

In order to achieve the object stated above, in the angle detectionmethod for bending machines according to the invention of claim 1,detection light is emitted toward a measurement object from a lightsource provided in an angle sensor equipped with a plurality of opticalsensors arranged at mutually opposite positions with the light sourcetherebetween, the angle sensor is rotated in the forward and reversedirections within the plane where the light source and optical sensorsare arranged, and the angle of the measurement object is detected basedon the rotation angle of the angle sensor at the time when the quantityof light received by one of the optical sensors is a maximum and therotation angle of the angle sensor at the time when the quantity oflight received by the other optical sensor is a maximum.

Accordingly, detection light emitted from the light source of therotating angle sensor impinges onto the measurement object and thereflected light therefrom is received by the plurality of opticalsensors positioned on opposite sides with the light source therebetween,and the angle of the measurement object is measured from the angles of )the angle sensor at the positions where the quantity of light receivedby each of the optical sensors forms a peak. That is, in an examplestructure where the optical sensors are positioned symmetrically atequal distances from the light source, the angle of the detection objectcan be detected from the fact that the detection light impinges ontoperpendicular to the detection object at an intermediate rotation angleposition of the angle sensor between the positions where the quantity oflight received by each of the optical sensors is a maximum.

In the angle detection method for bending machines according to theinvention of claim 2, detection light is emitted toward a measurementobject from a light source provided in an angle sensor equipped with atleast one pair of optical sensors arranged at symmetrical positions withthe light source centered therebetween, the angle sensor is rotated inthe forward and reverse directions within the plane where the lightsource and optical sensors are arranged, and the angle of themeasurement object is detected based on the rotation angles of the anglesensor from a reference position when the quantities of light receivedby the pair optical sensors are the same.

Accordingly, detection light emitted from the light source of therotating angle sensor strikes the measurement object and the reflectedlight therefrom is received by the pair of optical sensors symmetricallypositioned at equally distances from the light source, and the angle ofthe measurement object is measured from the rotation angle of the anglesensor at the time when the quantities of light received by the pair ofoptical sensors are the same. That is, the angle of the detection objectis detected from the fact that the detection light from the light sourceis incident perpendicular on the detection object when the same quantityof light is received by each of the optical sensors arrangedsymmetrically at equal distances from the light source.

In the angle detection apparatus according to the invention of claim 3,the apparatus includes an angle sensor equipped with a light source foremitting detection light toward a measurement object and a plurality ofoptical sensors for receiving reflected light from the measurementobject, the optical sensors being located at mutually opposite positionswith the light source arranged therebetween, and the angle sensor beingrotatable in forward and reverse directions in the plane where the lightsource and the optical sensors are arranged; a rotation angle detectorfor detecting the rotation angle of the angle sensor with respect to aprescribed reference position; a peak value detection portion fordetecting the peak value of the reflected light received by the opticalsensors; and an angle calculation portion for calculating the angle ofthe measurement object based on those rotation angles of the anglesensor detected by the rotation angle detector which should correspondto the peak values detected by the peak value detection portion.

Accordingly, detection light is emitted toward the measurement objectfrom the light source while the angle sensor is rotated in the forwardand reverse directions, and the light reflected from the measurementobject is received by the plurality of optical sensors provided atsymmetrical positions with respect to the light source. The quantity oflight received at this time is synchronized with the rotation angle ofthe angle sensor detected by the rotation angle detector and held forfuture use, and based on the data of this quantity of received light,the peak value detection portion detects the peak value of the quantityof received light. Then, the rotation angles of the angle sensorcorresponding to the peak values of each optical sensor are detected bythe rotation angle detector, and the angle calculation portion performscalculations based on these rotation angles to determine the angle ofthe measurement object.

In the angle detection apparatus according to the invention of claim 4,the apparatus includes an angle sensor equipped with a light source foremitting detection light toward a measurement object and at least onepair of sensors for receiving reflected light from the measurementobject, the pair of sensors being located at symmetrical positions withthe light source arranged in the center, and the angle sensor beingrotatable in forward and reverse directions in the plane where the lightsource and each of the sensors are arranged; a rotation angle detectorfor detecting the rotation angle of the angle sensor with respect to aprescribed reference position; and an angle calculation portion forcalculating the angle of the measurement object based on the rotationangle of the angle sensor detected by the rotation angle detector whenthe quantities of the reflected light received by each of the pair ofsensors are equal to each other.

Accordingly, detection light is emitted toward the measurement objectfrom the light source while the angle sensor is rotated in the forwardand reverse directions, and the light reflected from the measurementobject is received by the at least one pair of optical sensors providedat symmetrical positions with respect to the light source. Then therotation angle detector detects the rotation angle of the angle sensorat the time when the quantities of light received by the pair of opticalsensors are the same, and based on this rotation angle the anglecalculation portion detects the angle of the measurement object.

In the invention according to claim 5, the angle sensor in the angledetection apparatus stated in claim 3 or 4 is provided so as to beposition adjustable in a direction orthogonal to the bending line of themeasurement object.

Accordingly, the angle sensor can be positioned at that optimum positionwith respect to the final bending angle of the measurement object(workpiece), and the bending angle can be detected by such angle sensor.

In the invention according to claim 6, the angle sensor in the angledetection apparatus stated in claim 3, 4 or 5 is provided so as to beposition adjustable in a direction parallel to the bending line of themeasurement object.

Accordingly, even in the case where the length of the bending line ofthe measurement object changes, it is possible to position the anglesensor at positions such as both left and right edge portions and thecenter portion of the measurement portion, and this makes it possible todetect the bending angle at a plurality of locations of the measurementportion.

In the invention according to claim 7, an angle sensor includes a lightsource for emitting detection light toward a measurement object, and aplurality of optical sensors for receiving reflected light from themeasurement object, with the optical sensors being located at mutuallyopposite positions with the light source arranged therebetween.

Accordingly, the reflected light of the detection light emitted towardthe measurement object from the light source can be simultaneouslydetected with the plurality of optical sensors, and by rotating theangle sensor in the forward and reverse directions, it becomes possibleto detect the positions where the quantity of light received by each ofthe optical sensors is a maximum.

In the angle detection method for bending machines according to theinvention of claim 8, detection light is emitted toward a detectionobject from a light source provided in an angle sensor, whichsimultaneously emits detection light and receives reflected light, whilethe angle sensor is rotated around a rotation axis parallel to thebending line of the detection object; the maximum quantity of receivedlight of the reflected light from the detection object and the rotationangle of the angle sensor at that time are calculated; and the angle ofthe detection object is detected from the rotation angle at that time.

Accordingly, as soon as the detection light from the rotating anglesensor is emitted toward the detection object, reflected light from thedetection object is received along the same axis, and this makes itpossible to calculate the angle of the detection object from therotation angle of the angle sensor when the quantity of received lightis a maximum.

In the angle detection apparatus according to the invention of claim 9,the apparatus includes an angle sensor equipped with a light source foremitting detection light toward a detection object and an optical sensorfor receiving reflected light from the detection object, the anglesensor being rotatable around a rotation axis parallel to the bendingline of the detection object; a rotation angle detector for detectingthe rotation angle of the angle sensor with respect to a prescribedreference position; a maximum received light quantity detection portionfor detecting the maximum received light quantity of the reflected lightreceived by the optical sensor; a maximum received light quantity angledetection portion for detecting the rotation angle of the angle sensorat the time when the maximum received light quantity is obtained by themaximum received light quantity detection portion; and an anglecalculation portion for calculating the angle of the detection objectfrom the rotation angle obtained by the maximum received light quantityangle detection portion.

Accordingly, detection light from the light source is emitted toward thedetection object while the angle sensor is being rotated, and at thesame time, the optical sensor positioned on the same axis receivesreflected light from the detection object. The maximum of this quantityof received light is detected by the maximum received light detectionportion, and when the maximum received light is detected, the rotationangle of the angle sensor at that time is detected by the maximumreceived light quantity angle detection portion. Then, the anglecalculation portion determines the angle of the detection object byperforming calculations based on the obtained rotation angle of theangle sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an angle detection apparatus forbending machines according to this invention.

FIG. 2 is a flow chart showing the steps of an angle detection methodfor bending machines according to this invention.

FIG. 3 is a side view showing the structure and operation of a sensorhead.

FIGS. 4(A) and 4(B) are explanatory drawings showing the motion of thedetection light in the sensor head.

FIG. 5 is a graph showing the changes in the quantity of light receivedby light receivers for the rotation angles of the sensor head.

FIG. 6 is an explanatory drawing showing the operation of the sensorhead in the angle detection apparatus.

FIG. 7 is an explanatory drawing showing a second embodiment of thesensor head portion in the angle detection apparatus.

FIG. 8 is a block diagram showing the angle detection apparatus forbending machines according to this invention.

FIG. 9 is a flow chart showing the steps of an angle detection methodfor bending machines according to this invention.

FIG. 10 is a side view showing the structure and operation of a sensorhead.

FIG. 11 is an explanatory drawing showing the principle of the angledetection method for bending machines and the angle detection apparatusthereof.

FIG. 12 is a graph showing the changes in the quantity of light receivedfor the rotation angles of the sensor head.

FIG. 13 is an explanatory drawing showing a prior art angle detectionmethod for bending machines and the angle detection apparatus thereof.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, examples of preferred embodiments of the invention will bedescribed based on the drawings. Now, because the angle detection methodfor bending machines and the angle detection apparatus and angle sensorthereof according to the present invention are applied to a commonlyused processing machine such as a press brake for example, a detaileddescription of such a processing machine will be omitted.

FIG. 3 shows a sensor head 3 which serves as an angle sensor in an angledetection apparatus 1 for bending machines according to the presentinvention. In FIG. 3, the sensor head 3 is provided on top of a die base5 for mounting a die D which carries out a bending process on aworkpiece W which is the measurement object, in cooperation with a punchP. By means of a rotational drive unit (omitted from the drawings) suchas a pulse motor for example, the sensor head 3 is provided so as to befreely rotatable around a rotation axis RC (see FIG. 6) which isparallel to the lengthwise direction of the die D and punch P, namely,the bending line of the workpiece W. Further, the sensor head 3 isprovided so as to be freely movable in the bending line direction (thedirection normal to the plane of FIG. 3) by means of a moving deviceomitted from the drawings.

As shown in FIGS. 4(A) and (B), a light projector 9 comprised of a lightsource which emits a laser beam BM as detection light along a directionorthogonal (vertical direction) to a front surface 7 of the sensor head3 is provided in the center of the front surface 7. Further, a firstlight receiver 11 and a second light receiver 13 comprised of opticalsensors are provided on the front surface 7 of the sensor head 3 atequally distant positions from the light projector 9 so that the lightprojector 9 is interposed therebetween.

That is to say, the light source 9 and the plurality of optical sensors11, 13 are arranged in the same plane which includes the optical axis ofthe laser beam BM emitted from the light source 9, and the sensor head 3is provided so as to be rotatable in this plane.

In the present embodiment, even though the optical sensors 11, 13 wereprovided at equally distant symmetrical positions with the light source9 in between, the optical sensors 11, 13 are not necessarily limited tosymmetrical positions, and if they are positioned at mutually oppositepositions with the light source 9 in between, with the distance from thelight source 9 to the each of the optical sensors 11, 13 being known inadvance, each of optical sensors 11, 13 can be utilized to detect thebending angle of the workpiece W.

With FIG. 6 also used as reference, it can be seen that the rotationaxis RC intersects with and is orthogonal to the optical axis of thelaser beam BM emitted from the light projector 9, and this laser beam BMaxis is provided so as to be perpendicular to the plane that includesthe light projector 9, the first light receiver 11 and the second lightreceiver 13. Also, the sensor head 3 is rotated around this rotationaxis RC by means of a drive unit omitted from the drawings.

Next, with reference to FIG. 1, a description will be given for thestructure which functions as the control system of the angle detectionapparatus 1 for bending machines. The first light receiver 11 and thesecond light receiver 13 are connected to a light receiver change-overswitch 19 respectively through preamplifiers 15 and 17, and receivedlight signals from the first light receiver 11 or the second lightreceiver 13 are selected by means of this light receiver change-overswitch 19. Then, after this selected reception signal is sent through aband pass filter 21, with only a prescribed frequency width signalpassing therethrough, it is amplified by an amplifier 23 and inputtedinto a synchronous read circuit 25.

The synchronous read circuit 25 causes the received light data to bestored in a first received light data memory 27 or a second receivedlight data memory 29 in synchronism with the projection of light of thelaser beam BM from the light projector 9. And based on this receivedlight data, a peak value detection portion 31 detects the peak value ofthe received light signal. Further, by calculating the rotation angle ofthe sensor head 3 with a rotation angle detector 33, an anglecalculation portion 35 determines the bending angle of the workpiece W.

That is to say, when a signal indicating the completion of the bendingprocess has been received from a control device which controls thebending processing machine such as a press brake, a measurement controlportion 37 sends out a light receiver selection signal to the lightreceiver change-over switch 19 to select the first light receiver 11 orthe second light receiver 13, and a one-step drive is carried out byrotating the sensor head 3 by a prescribed rotation angle, and aone-step drive completion signal is sent to the synchronous read circuit25 so that the received light data sampling are synchronized with therotation angle of the sensor head 3. The synchronous read circuit 25 issynchronized with a modulation signal of a modulator 39.

Next, with reference to FIG. 4 and FIG. 5, a description will be givenfor the principle of detecting the bending angle 2 θ of the workpiece W.

With reference to FIG. 4(A), when the sensor head 3 is rotated as shownin the drawing to a position where the rotation angle is θ 1, the laserbeam BM impinging onto the surface of the workpiece W from the lightprojector 9 is reflected, and the first light receiver 11 receives amaximum amount of such reflected light. With reference to FIG. 4(B),when the sensor head 3 is moved in a similar manner to a position wherethe rotation angle is θ 2, the second light receiver 13 receives amaximum amount of such reflected light. Further, FIGS. 4(A) and (B) showthe case where an angle of 0 degrees (namely, a horizontal state) formsthe reference.

FIG. 5 shows the changes in the quantity of received reflected lightthat occur at this time with respect to the rotation angle of the sensorhead 3, and in general the amount of reflected light received by thefirst light receiver 11 is a maximum when the tilt angle of the sensorhead 3 is at θ 1 in the counter-clockwise direction with respect to areference angle θ (where θ=0 degrees in the example shown in FIG. 4),and the amount of reflected light received by the second light receiver13 is a maximum when the tilt angle of the sensor head 3 is at θ 2 inthe clockwise direction with respect to the reference angle θ.

As described above, because the first light receiver 11 and the secondlight receiver 13 are provided at equal distances from the lightprojector 9, at an intermediate position in FIG. 5 between the rotationangle θ 1 measured from the horizontal position (i.e., θ=0), where theamount of light received by the first light receiver is a maximum, andthe rotation angle θ 2 measured from the horizontal position, where theamount of light received by the second light receiver is a maximum, thelaser beam BM is projected perpendicular with respect to the workpiece Wwhich has undergone a bending process. In this way, the angle θ of thebent workpiece W can be obtained from

θ=(θ1+θ2)/2.

In this regard, θ 1 and θ 2 will be positive for the clockwise directionand negative for the counter-clockwise direction.

Next, with reference to FIGS. 1 and 6 as well as FIG. 2, a descriptionwill be given for a method of determining the bending angle of aworkpiece W using the angle detection apparatus 1 described above.

First, when the angle detection operation is started (Step SS), duringthe bending process, the sensor head 3 is moved by a moving device(omitted from the drawings) along a direction parallel to the bendingline to a measuring position (Step S1). In view of a target bendingangle of 2 θ, the sensor head 3 is rotated by θ−α (see FIG. 6) aroundthe rotation axis RC to prepare for angle detection operations (StepS2). In this regard, when setting a target bending angle θ, a springback amount is taken into consideration so that the workpiece W isreliably set within the interval θ±α.

When the bending process is completed (Step S3), the measurement controlportion 37 outputs a first light receiver selection signal to the lightreceiver change-over switch 19 to select the first light receiver 11(Step S4). The sensor head 3 which is at the measurement starting angleposition θ−α is rotated by a prescribed angle in the clockwise directionin one step by a rotational driving device (omitted from the drawings)(Step S5). At this time, a one-step driving completion signal is sent tothe synchronous read circuit 25 from the measurement control portion 37,so that at the same time the sensor head 3 is being rotated, the amountof light received by the first light receiver 11 is measured and storedas data in the first received light data memory 27 (Step S6).

Until the rotation angle of the sensor head 3 reaches θ+α, the processis repeated from Step 5, and when the rotation angle reaches θ+α (StepS7), the measurement control portion 37 outputs a second light receiverselection signal to the light receiver change-over switch 19 to selectthe second light receiver 11 (Step S8). In this regard, the value of ais set in accordance with the distance between the light projector 9 andthe first and second light receivers 11, 13 and the distance between thesensor head 3 and the workpiece W being measured, for example, at around10 degrees.

The sensor head 3, which was rotationally moved to the position θ+α inorder to carry out measurements with the first light receiver 11, isrotated by a prescribed angle in the counter-clockwise direction in onestep by the rotational driving device (Step S9). At this time, aone-step driving completion signal is sent to the synchronous readcircuit 25 from the measurement control portion 37, so that at the sametime the sensor head 3 is being rotated, the amount of light received bythe second light receiver 13 is measured and stored as data in thesecond received light data memory 29 (Step S10).

Until the rotation angle of the sensor head 3 reaches θ−α, the processis repeated from Step 9, and when the rotation angle reaches θ−α (StepS11), the peak value detection portion 31 retrieves the peak values ofthe quantity of light received by the first light receiver 11 from thedata sequence stored in the first received light data memory 27 (StepS12). In a similar manner, the peak values of the quantity of lightreceived by the second light receiver are retrieved from the datasequence stored in the second received light data memory 29 (Step S13).

From the angle θ 1 of the sensor head 3 which corresponds to the peakvalue of the first light receiver 11 and the angle θ 2 of the sensorhead 3 which corresponds to the peak value of the second light receiver13 obtained in this way, the angle calculation portion 35 calculates thebending angle θ of the workpiece W (Step S14), and then the angledetection operation is completed (Step SE).

The present invention is not limited to the embodiment described above,and by carrying out appropriate modifications, the present invention canbe executed in other ways. That is to say, in the embodiment describedabove, although the sensor head 3 was provided on top of the die base 5so as to be movable in the direction of the bending line and rotatable,it is also possible to mount the sensor head 3 on the head of the pressbrake so as to be movable in the up and down direction and the front andback direction. In this way, it is possible to measure a wider range ofbending angles.

That is to say, as shown in FIG. 7, by providing the die base 5 or aposition nearby with a guide portion 37 which runs parallel to thebending line of the workpiece W, by arranging a movement positioningmember 39, equipped with a plurality of vertically erect guide rods 41and an erect screw 43, to be movable along the guide portion 37, and byproviding a support member 47, which supports the sensor head 3, with arotatable nut member 45 screwed onto the screw 43 so as to be movable inthe up and down direction, it becomes possible to construct an apparatuswhich can adjust the position of the sensor head 3 in the up and downdirection, and this makes it possible to carry out a detection of thebending angle of the workpiece W with the sensor head 3 positioned at anoptimum height position with respect to the bending angle of theworkpiece W.

Further, in the description stated above, although the bending angle ofthe workpiece W was detected by calculating the intermediate positionbetween the rotational position of the sensor head 3 when the quantityof light received by the first light receiver 11 shows a peak value andthe rotational position of the sensor head 3 when the quantity of lightreceived by the second light receiver 13 shows a peak value, bydetecting the rotational position of the sensor head 13 when thequantities of light received by the first and second light receivers 11,13 are the same as each other, it is possible to detect the bendingangle of the workpiece W based on this rotational position.

A structure for the case stated above can be easily constructed byarranging the first and second light receivers 11, 13 to measure thereflected light from the laser beam impinging onto the workpiece W, byproviding a comparison means which carries out a comparison to determinewhether or not the detection values of the first and second lightreceivers 11, 13 are the same, and by driving a motor in the forward orreverse direction until the comparison results of the comparison meansindicate equal detection values.

FIGS. 8˜12 show a second embodiment of the present invention.

In FIG. 10, a sensor head 53 of an angle detection apparatus 51 isprovided on top of a die base 55 for mounting a die D which carries outa bending process on a workpiece W which is the measurement object, incooperation with a punch P. The sensor head 53 is provided so that bymeans of rotational drive of a motor M described below (see FIG. 8), itis freely rotatable around a rotation axis RC (see FIG. 11) which isparallel to the lengthwise direction of the die D and punch P, namely,the bending line of the workpiece W. Further, the sensor head 53 isprovided so as to be freely movable in the bending line direction (thedirection normal to the plane of FIG. 10) by means of a moving device(omitted from the drawings).

With reference to FIG. 8 as well as the foregoing, in the sensor head53, a laser beam BM emitted from a light source 57 is formed intoparallel rays of light by a collimator 59, which are then passed througha beam splitter 61 and aimed as detection light at a workpiece W whichis the measurement object.

The light reflecting off the workpiece W forms a reflected light beamRBM the direction of which is changed by a beam splitter 61 and then bya reflection mirror 63; then, only the light which is in a prescribedrange is selected and converted into electrical signals by an opticalfilter 65 and a detector 67 such as a photodiode as an optical sensor.The electrical signals are then sent out as received light signals.

From the received light signals obtained in this way, only those signalsthat have a prescribed frequency width will be passed through by a bandpass filter 69, amplified by an amplifier 71 and then inputted into asynchronous read circuit 73, where they are designed to be synchronizedwith emission signals of the laser beam BM from the light source 57 sentin via a modulator 75.

The received light signals synchronized by the synchronous read circuit73 with the emission of the laser beam BM are sent to a comparator 77 toselect the maximum received light signal, which is then stored in amaximum value memory 59 forming a maximum received light quantitydetection portion and sent to a rotation angle detector 81 such as anencoder provided in a servo motor M for rotating the sensor head 53, andthen the rotation angle of the sensor head 53 at this time is detectedand stored in an angle memory 83 which is a maximum received lightquantity angle detection portion as well as an angle calculationportion.

That is to say, when a drive circuit 85 receives a signal indicating thecompletion of the bending process from a control device which controlsthe press brake, the motor M is controlled and a one-step drive iscarried out by rotating the sensor head 53 by a prescribed rotationangle. And at the same time a one-step drive completion signal is sentto the comparator 77 wherein the received light signal at this time iscompared with the previous received light signal in synchronism with therotation angle of the sensor head 53, whereby the maximum received lightsignal is stored in the maximum value memory 79, and the rotation angleof the sensor head 53 in stored in the angle memory 83.

Next, with reference to FIG. 11, a description will be given for theprinciple of detecting the bending angle 2 θ of the workpiece W.

When a laser beam BM which forms detection light is aimed at a workpieceW which has been subjected to a bending process, the amount of reflectedlight received by the sensor head 53 will change in accordance with theincidence angle with respect to the surface of the workpiece W. Fromthis fact, after the completion of the bending process of the workpieceW, the laser beam is aimed at the workpiece W while the sensor head 53is rotated within a range ±α (here, α lies in a range of about 5˜10degrees, for example) with respect to the target bending angle θ todetermine the distribution of the quantity of light received by thesensor head 53.

As is made clear with reference to FIG. 11, in the case where the laserbeam BM emitted from the sensor head 53 is perpendicular to the surfaceof the workpiece W, the reflected light beam RBM follows the same pathand is received by the sensor head 53.

With a combined reference to FIG. 12, in the distribution of thequantity of received light determined as described above, it is knownthat a maximum peak is obtained when the laser beam BM is aimedperpendicular at the workpiece W. Accordingly, the rotation angle of thesensor head 53 corresponding to the maximum peak can be determined, andbased on this rotation angle it becomes possible to detect the bendingangle θ of the workpiece W. At this point, it need not be said that thebending angle is actually 2 times θ.

Next, based on FIG. 9, a description will be given for a method ofdetermining the bending angle of a workpiece W using the angle detectionapparatus 51 for bending machines described above.

When the angle detection operation is started (Step SS), during thebending process, the sensor head 53 is moved along a direction parallelto the bending line to a measuring position (Step SS1). In view of atarget bending angle of 2 θ, the motor M rotates the sensor head 53 byθ−α to prepare for the start of measurements (Step SS2). Further, themaximum value memory 79 and the angle memory 83 are cleared to zero(Step SS3).

A judgement as to whether or not the bending process has been completedis carried out (Step SS4), and if judged completed, the program proceedsto measurements. The reflected light beam RBM of the laser beam BMemitted toward the workpiece W from the sensor head 53 is received, andthe quantity of received light is measured (Step SS5). The measuredquantity of received light is then compared with the maximum value up tothat point (Step SS6), and in the case where the measured quantity ofreceived light is larger than the maximum value up to that point, themaximum value memory 79 is updated with the current detected quantity ofreceived light, and at the same time the angle memory 83 is updated withthe current rotation angle of the sensor head 53 (Step SS7).

On the other hand, in the case where at Step SS6 the measured quantityof received light is not larger than the maximum value up to that point,or after updating the maximum value at Step SS7, the rotation angle ofthe sensor head 53 is judged whether it is equal to θ+α (Step SS8) andif it is smaller than θ+α, the sensor head 53 undergoes a one-steprotation and the program returns to Step SS5, with the steps from therebeing repeated (Step SS9).

In the case where the rotation angle of the sensor head 53 reaches θ+α,the bending angle 2 θ of the workpiece W is calculated from the rotationangle stored in the angle memory 83 (Step SS10), and then the angledetection operation is terminated (Step SE).

Now, in the embodiment described above, although the sensor head 53 wasprovided on top of the die base 55 so as to be movable in the directionof the bending line and rotatable, it is also possible to mount thesensor head 53 on the bed of the press brake so as to be movable in theup and down direction and the front and back direction. In this way, itis possible to measure a wider range of bending angles.

Further, in another method, all the measured values are stored, and thenafter the measurements have been completed, the stored data isseparately plotted on a curve, with the maximum quantity of receivedlight obtained from this curve being used to calculate the correspondingangle. In this method, an angle measurement at an accuracy below themeasured rotational angle of the sensor head 53 is possible. Further, inthe present invention, although measurements were carried out underpressing conditions by means of the punch and die, the conditions underwhich measurements are carried out are not limited to this condition.

Furthermore, in the case where the reflectance is small due to surfaceconditions of the workpiece, it is possible to obtain a good reflectanceby carrying out an appropriate process such as applying an appropriatereflecting tape for example, and it becomes possible to execute thepresent invention regardless of the effects of surface conditions of theworkpiece.

The present invention is not limited to the embodiment described above,and by carrying out appropriate modifications, the present invention canbe executed in other ways. For example, it is possible to form astructure which uses a transmitter to transmit appropriateelectromagnetic waves or ultrasound waves and a receiver in place of thelight projector and light receiver.

In this case, the apparatuses shown in FIGS. 1 and 8 are modified toreplace the structure related to the optical system with a structurecorresponding to electromagnetic waves or ultrasound waves, in which theangle detection apparatus includes an angle sensor equipped with atransmission source for emitting detection waves toward a measurementobject and a plurality of sensors for receiving reflected waves from themeasurement object, the sensors being located at mutually oppositepositions with the transmission source arranged therebetween, and theangle sensor being rotatable in forward and reverse directions in theplane where the transmission source and each of the sensors arearranged; a rotation angle detector for detecting the rotation angle ofthe angle sensor with respect to a prescribed reference position; a peakvalue detection portion for detecting the peak value of the reflectedwave received by the optical sensors; and an angle calculation portionfor calculating the angle of the measurement object based on therotation angle of the angle sensor detected by the rotation angledetector which should correspond to the peak value detected by the peakvalue detecting portion.

Further, it is possible to construct an angle detection apparatus whichincludes an angle sensor equipped with a transmission source foremitting detection waves toward a measurement object and at least onepair of sensors for receiving reflected waves from the measurementobject, the pair of sensors being located at symmetrical positions withthe transmission source arranged in the center, and the angle sensorbeing rotatable in forward and reverse directions in the plane where thetransmission source and each of the sensors are arranged; a rotationangle detector for detecting the rotation angle of the angle sensor withrespect to a prescribed reference position; and an angle calculationportion for calculating the angle of the measurement object based on therotation angle of the angle sensor detected by the rotation angledetector when the intensities of the reflected waves received by each ofthe pair of sensors are equal to each other.

Further, it is also possible to construct an angle detection apparatuswhich includes an angle sensor equipped with a transmission source foremitting detection waves toward a detection object and sensors forreceiving reflected waves from the detection object, the angle sensorbeing rotatable around a rotation axis which is parallel to the bendingline of the detection object; a rotation angle detector for detectingthe rotation angle of the angle sensor with respect to a prescribedreference position; a peak value detection portion for detecting thepeak value of the reflected wave received by the sensors; an angledetection portion for detecting the rotation angle of the angle sensorwhen the peak value is obtained by the peak value detection portion; andan angle calculation portion for calculating the angle of the detectionobject from the rotation angle obtained by the angle detection portion.

Also, in the angle sensor equipped with a transmission source forimpinging detection waves onto the measurement object and sensors forreceiving the reflected waves from the measurement object, suchstructure can be equipped with a plurality of sensors arranged atmutually opposite positions with the transmission source therebetween.

APPLICABILITY TO INDUSTRY

As described above, in the angle detection method for bending machinesaccording to the invention of claim 1, detection light emitted from thelight source of the rotating angle sensor strikes the measurement objectand the reflected light therefrom is received by optical sensorspositioned at mutually opposite positions in the angle sensor with thelight source therebetween, and the angle of the measurement object ismeasured from the rotation angles of the angle sensor at the positionswhere the quantity of light received by each of the optical sensorsforms a peak. Namely, because angle detection is carried out by anon-contact type angle sensor, there is no risk of external forcesdeforming the workpiece as in the prior art, and this makes it possibleto carry out a highly accurate angle detection. Further, because thereis no need for expensive devices such as imaging devices, the entireapparatus can be constructed at a low cost.

In the angle detection method for bending machines according to theinvention of claim 2, detection light emitted from the light source ofthe rotating angle sensor strikes the measurement object and thereflected light therefrom is received by a pair of optical sensorssymmetrically positioned in the angle sensor at equally distances fromthe light source, and the angle of the measurement object is measuredfrom the rotation angle of the angle sensor at the time when thequantities of light received by the pair of optical sensors are the sameas each other. Namely, because angle detection is carried out by anon-contact type angle sensor, there is no risk of external forcesdeforming the workpiece as in the prior art, and this makes it possibleto carry out a highly accurate angle detection. Further, because thereis no need for expensive devices such as imaging devices, the entireapparatus can be constructed at a low cost.

In the angle detection apparatus for bending machines according to theinvention of claim 3, detection light is directed onto the measurementobject from a light source while an angle sensor is rotated in theforward and reverse directions, and the light reflected from themeasurement object is received by a plurality of optical sensorsprovided at mutually opposite positions with the light source arrangedtherebetween. The quantity of light received at this time issynchronized with the rotation angle of the angle sensor detected by therotation angle detector and held for future use, and based on the dataof this quantity of received light, the peak value detection portiondetects the peak value of the quantity of received light, and because anangle detector determines the angle of the measurement object bycalculations based on the rotation angles of the angle sensorcorresponding to the peak values for each optical sensor, there is norisk of deformation of the workpiece due to direct or indirect contactas in the prior art, and this makes it possible to carry out a highlyaccurate angle detection. Further, because there is no need forexpensive devices such as imaging devices, the entire apparatus can beconstructed at a low cost.

In the angle detection apparatus for bending machines according to theinvention of claim 4, detection light is directed onto the measurementobject from a light source while an angle sensor is rotated in theforward and reverse directions, and the light reflected from themeasurement object is received by at least one pair of optical sensorsprovided at symmetrical positions with respect to the light source, witha rotation angle detector detecting the rotation angle of the anglesensor at the time when the quantities of light received by the pair ofoptical sensors are the same as each other, and because an anglecalculation portion detects the angle of the measurement object based onthis rotation angle, there is no risk of deformation of the workpiecedue to direct or indirect contact as in the prior art, and this makes itpossible to carry out a highly accurate angle detection. Further,because there is no need for expensive devices such as imaging devices,the entire apparatus can be constructed at a low cost.

In the invention according to claim 5, because the angle sensor of theangle detection apparatus stated in claim 3 or 4 is provided so as to beposition adjustable in a direction orthogonal to the bending line of themeasurement object, the angle sensor can be positioned at an optimumposition with respect to the final bending angle of the measurementobject (workpiece), and this makes it possible to obtain good accuracyfor various bending angles.

In the invention according to claim 6, because the angle sensor of theangle detection apparatus stated in claim 3, 4 or 5 is provided so as tobe position adjustable in a direction parallel to the bending line ofthe measurement object, it becomes possible for the angle sensor toeasily carry out detection of the bending angle for a plurality oflocations such as both left and right edge portions and the centerportion of the measurement object.

In the invention according to claim 7, because an angle sensor isequipped with a light source for emitting detection light toward ameasurement object and a plurality of optical sensors for receivingreflected light from the measurement object, with the optical sensorsbeing located at mutually opposite positions with the light sourcearranged therebetween, it is possible to simultaneously detect thereflected light of the detection light directed onto the measurementobject from the light source with the plurality of optical sensors, andin the case where the angle sensor is rotated in the forward and reversedirections, it becomes possible to separately detect the peak value ofeach of optical sensors.

In the angle detection method for bending machines according to theinvention of claim 8, detection light from a light source of a rotatingangle sensor is emitted toward a detection object, while at the sametime reflected light from the detection object is received along thesame axis, and because the angle of the detection object is calculatedfrom the rotation angle of the angle sensor when the quantity ofreceived light forms a maximum, it is possible to carry out angledetection with a non-contact type angle sensor, thereby eliminating therisk of external forces deforming the workpiece as in the prior art, andbecause there is also no risk of the adjustment state changing overtime, this apparatus makes it possible to carry out a highly accurateangle detection. Further, because there is no need for expensive devicessuch as imaging devices, the entire apparatus can be constructed at alow cost.

In the angle detection apparatus for bending machines according to theinvention of claim 9, detection light from a light source is directedonto a detection object while an angle sensor is being rotated, and atthe same time an optical sensor positioned on the same axis receivesreflected light from the detection object. The maximum of this quantityof received light is detected by a maximum received light detectionportion, and when the maximum received light is detected the rotationangle of the angle sensor at that time is detected by a rotation angledetector, and because an angle calculation portion determines the angleof the detection object by calculations based on the obtained rotationangle of the angle sensor, there is no risk of deformation of theworkpiece due to direct or indirect contact as in the prior art, andbecause there is also no risk of the adjustment state of the sensoritself changing over time, this apparatus makes it possible to carry outa highly accurate angle detection. Further, because there is no need forexpensive devices such as imaging devices, the entire apparatus can beconstructed at a low cost.

What is claimed is:
 1. An angle detection method for bending machines,comprising the steps of emitting detection light toward a measurementobject from a light source provided in an angle sensor equipped with aplurality of optical sensors arranged at mutually opposite positionswith the light source therebetween, rotating the angle sensor in theforward and reverse directions within the plane where the light sourceand optical sensors are arranged, and detecting the angle of themeasurement object based on the rotation angle of the angle sensor atthe time when the quantity of light received by one of the opticalsensors is a maximum and the rotation angle of the angle sensor at thetime when the quantity of light received by the other optical sensor isa maximum.
 2. An angle detection method for use in bending machines,comprising: emitting detection light toward a measurement object from alight source provided in an angle sensor equipped with at least one pairof optical sensors arranged at substantially symmetrical positions withthe light source substantially centered therebetween; rotating the anglesensor in forward and reverse directions within a plane where the lightsource and optical sensors are arranged; detecting peak values ofreflected light received by the respective optical sensors; anddetecting an angle of the measurement object based on the rotation angleof the angle sensor from a reference position when the quantities oflight received by the pair of optical sensors are substantially thesame.
 3. An angle detection apparatus, comprising; an angle sensorequipped with a light source for emitting detection light toward ameasurement object and at least one pair of sensors for receivingreflected light from the measurement object, said pair of sensors beinglocated at symmetrical positions with the light source arranged in thecenter, and said angle sensor being rotatable in forward and reversedirections in a plane where the light source and each of said sensorsare arranged; a peak value detection portion for detecting peak valuesof the reflected light respectively received by said optical sensors; arotation angle detector for detecting the rotation angle of the anglesensor with respect to a prescribed reference position; and an anglecalculation portion for calculating the angle of the measurement objectbased on the rotation angle of the angle sensor detected by the rotationangle detector when the quantity of the reflected light received by eachof the pair of sensors are equal to each other.
 4. An angle detectionapparatus, comprising an angle sensor equipped with a light source foremitting detection light toward a measurement object and a plurality ofoptical sensors for receiving reflected light from the measurementobject, the optical sensors being located at mutually opposite positionswith the light source arranged therebetween, and the angle sensor beingrotatable in forward and reverse directions in the plane where the lightsource and the optical sensors are arranged; a rotation angle detectorfor detecting the rotation angle of the angle sensor with respect to aprescribed reference position; a peak value detection portion fordetecting the peak values of the reflected light received by the opticalsensors; and an angle calculation portion for calculating the angle ofthe measurement object based on those rotation angle of the angle sensordetected by the rotation angle detector which correspond to the peakvalues detected by the peak value detection portion.
 5. The angledetection apparatus as stated in claim , wherein the angle sensor isprovided so as to be position adjustable in a direction orthogonal tothe bending line of the measurement object.
 6. The angle detectionapparatus as stated in claim 4, wherein the angle sensor is provided soas to be position adjustable in a direction parallel to the bending lineof the measurement object.
 7. An angle sensor, comprising: a lightsource for emitting detection light toward a measurement object; aplurality of optical sensors for receiving reflected light from themeasurement object, said optical sensors being located at mutuallyopposite positions with said light source arranged therebetween, saidoptical sensors and said light source being configured to collectivelyrotate about a common axis; and a peak value detection portion fordetecting peak values of the reflected light respectively received bysaid optical sensors.
 8. The angle sensor according to claim 7, furthercomprising a rotating angle detector that detects a rotation angle ofthe sensor with respect to a predetermined reference position.
 9. Anangle detection method for bending machines, comprising emittingdetection light toward a detection object from a light source providedin an angle sensor, the angle sensor simultaneously emitting detectionlight and receiving reflected light on plurality of optical sensors;rotating the angle sensor around a rotation axis parallel to a bendingline of the detection object; calculating the maximum quantity ofreceived light of the reflected light from the detection object and arotation angle of the angle sensor at a predetermined time; anddetecting the angle of the detection object from the rotation angle atthe predetermined time.
 10. The angle detection bending method accordingto claim 9, wherein the plurality of optical sensors are located atmutually opposite positions with the light source therebetween.
 11. Anangle detection apparatus, comprising an angle sensor equipped with alight source for emitting detection light toward a detection object anda plurality of optical sensors for receiving reflected light from thedetection object, the angle sensor being rotatable around a rotationaxis parallel to a bending line of the detection object; a rotationangle detector for detecting the rotation angle of the angle sensor withrespect to a prescribed reference position; a maximum received lightquantity detection system that detects the maximum received lightquantity of the reflected light received by said plurality of opticalsensors; a maximum received light quantity angle detection portion fordetecting the rotation angle of the angle sensor at the time when themaximum received light quantity is obtained by the maximum receivedlight quantity detection system; and an angle calculation system thatcalculates the angle of the detection object from the rotation angleobtained by the maximum received light quantity angle detection system.12. The angle detection apparatus according to claim 11, wherein saidplurality of optical sensors are located at mutually opposite positionswith the light source therebetween.